见代码

<?php
/**
 * StringUtils 类
 *
 * @package common\components
 * @author Frank
 * @email fengxuting@gmail.com
 * @version 1.0
 */
class StringUtils
{    
    /**
     * textarea 回车变换行
     */
    public static function textarear2br($str){

        $names = preg_split('/\r\n/',$str);
        $new_str = implode("<br/>",$names); ;
        return $new_str ;
    }
    /**
     * textarea 换行变回车
     */
    public static function textareabr2r($str){
        $names = preg_split('/<br\/>/',$str);
        $new_str = implode("\r",$names); ;
        return $new_str ;
    }
}

参考
http://www.jb51.net/article/56445.htm